A description will be made below of an outline of a wireless emergency service and a scenario of requesting and acquiring location information for a wireless emergency rescue service. Also, a conventional method for initially accessing and ranging with a Base Station (BS) at an MS will be described in brief.
Emergency services are intended to notify occurrence of emergencies to persons, countries, or communities and deal with the emergencies. For example, an emergency service provides a person in an emergency situation with a rescue operation and issues an emergency warning about a specific disaster area. There are largely two types of emergency services, wireless emergency rescue service and wireless emergency alert service.
The wireless emergency rescue service locates a wireless mobile communication user and provides safe rescue assistance to him, when a fire, a crime or any other emergency has occurred to him. The wireless emergency alert service alerts wireless subscribers within a specific geographical area of an upcoming storm, earthquake, tsunami, or Chemical, Biological and Radiological (CBR) accident by issuing an emergency notification. To issue the alert, a warning message is broadcast to all MSs located in the specific area. The wireless emergency alert service involves simple message broadcasting or detection of the locations of MSs, thus not imposing much load on a network.
However, a big problem is actually that when the network is overloaded with accessing users in a disaster or an exceptional situation, all MSs may be disconnected. In this case, services may not be provided normally to the MSs in a conventional technology. For example, when a disaster happens in a particular area, the number of calls increases in the disaster area and thus the network is congested with initially accessing users. This congestion may be controlled separately by a control operation at or above a Medium Access Control (MAC) layer and a physical-layer operation.
From the viewpoint of service flow, the use of resources at or above the MAC layer may be readily controlled according to the access feature of each subscriber. However, no restriction is imposed on the physical layer in an emergency situation, which leads to overheated competition for radio resources. The resulting resource dissipation causes network inefficiency. At worst, even MSs with high priority (e.g. governmental terminals, public institute terminals, etc.) cannot access the network.
With physical-layer limitations on support of emergency services, MSs may have difficulty in initial network entry and in inter-Radio Access Technology (RAT) handover. During initial ranging in which an MS attempts initial network entry, the MS suffers from jamming from other general MSs. Hence, the MS cannot detect signals or detects wrong parameters, which makes communication of the MS impossible. Even though signal detection is possible, a Base
Station (BS) keeps or releases connections only when it gets knowledge of the priority levels of MSs that attempt initial access by performing a predefined procedure. Accordingly, it may occur that network entry is impossible without an appropriate physical model for initial access.
The same thing applies to inter-RAT handover. If associated systems exchange all needed system information and thus an MS can perform an intra-RAT handover procedure immediately when it enters a target system, the problem may be avoided.
However, all procedures are performed, starting with initial ranging access even for the inter-RAT handover because specific physical/system parts such as initial access are not shared yet (not compatible in a specification phase). In case of high initial access load, even an MS with a high priority level may not enter the network.
However, there is no specified technique for requesting an emergency service to a BS during initial network access or in a connected state by an MS.